This invention relates to obstacle detection systems for vehicles. Such systems must alert a vehicle operator to the presence of near and distance objects and direct and reflected radiation must be employed.
In the prior art obstacle detection systems infrared and ultrasonic radiation generally have disadvantages that discourage their use. Microwave radiation on the other hand is commonly used in a variety of forms of radar systems, and the advantages of the microwave radar technology make it attractive for obstacle detection systems as well. See the article "Automotive Radar: A Brief Review" by D. M. Grimes and T. O. Jones in Proceedings of the IEEE, Jun., 1974, pp.804-822 and the relevant prior art literature cited therein.
The assigned microwave operating spectrum for radar, for example, is in the X-band, in the range of 8.0 to 12.0 GHz. A particular operating band applicable to obstacle detection systems has been set aside by the Federal Communications Commission in the range from 10.50 to 10.55 GHz. For this frequency range, microwave components are reasonable in cost and size; for example a planar antenna is approximately 1.times.2 inches in area. However, the limitations of this available bandwidth makes it difficult to achieve an adequate resolution of targets. For example, resolution below a minimum of 10 feet in distance is not readily obtainable with a limited bandwidth FM/CW radar system. Resolution of 5, 2.5 or even 0 feet would be advantageous for obstacle detection and warning for vehicles; yet it has not been available due to bandwidth limitations. Multiple obstacles should be detectable, but such a facility has not been available.